Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.

Quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in Lake Baikal, Siberia

Abstract: Endemic planktonic diatoms are a major component of Lake Baikal sediments during interglacial periods. To investigate how these diatom assemblages are altered during sediment formation, quantitative plankton monitoring (1995‐1998) was integrated with sediment trapping over 2 yr (1996‐1997) in Baikal’s southern basin (depth ;1,400 m). The traps consisted of both open (;6 monthly) and sequential (;2 weekly) collectors deployed throughout the water column. Sedimentation was seasonal, with diatom species composition, valve abundance, and total dry mass reflecting changes in the planktonic communities. Sedimented assemblages were transmitted largely intact to the deepest traps (;1,300‐1,390 m); some compositional blurring occurred from differential sinking rates and dissolution of diatom valves. A rapid mass flux event of Aulacoseira skvortzowii and A. baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d 21 and dry mass fluxes . 5gm 22 d 21 . Although dissolution was evident for all species, more delicate taxa were preferentially affected (e.g., A. skvortzowii vegetative cells and fineSynedra species), whereas Nitzschia acicularis valves were almost entirely dissolved within the water column. Comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment, with sedimentary diatom accumulation rates being only about 1% of trap deposition and plankton production rates. Dissolution was significant in explaining 5‐30% of species variance between all taphonomic levels (plankton, trap samples, and surface sediments). Results indicate that diatom-based paleoclimatic records in Lake Baikal sediments could be improved and refined by taking taphonomic considerations into account.

Beyond the Fe-P-redox connection: preferential regeneration of phosphorus from organic matter as a key control on Baltic Sea nutrient cycles

Abstract: . Patterns of regeneration and burial of phosphorus (P) in the Baltic Sea are strongly dependent on redox conditions. Redox varies spatially along water depth gradients and temporally in response to the seasonal cycle and multidecadal hydrographic variability. Alongside the well-documented link between iron oxyhydroxide dissolution and release of P from Baltic Sea sediments, we show that preferential remineralization of P with respect to carbon (C) and nitrogen (N) during degradation of organic matter plays a key role in determining the surplus of bioavailable P in the water column. Preferential remineralization of P takes place both in the water column and upper sediments and its rate is shown to be redox-dependent, increasing as reducing conditions become more severe at greater water-depth in the deep basins. Existing Redfield-based biogeochemical models of the Baltic may therefore underestimate the imbalance between N and P availability for primary production, and hence the vulnerability of the Baltic to sustained eutrophication via the fixation of atmospheric N. However, burial of organic P is also shown to increase during multidecadal intervals of expanded hypoxia, due to higher net burial rates of organic matter around the margins of the deep basins. Such intervals may be characterized by basin-scale acceleration of all fluxes within the P cycle, including productivity, regeneration and burial, sustained by the relative accessibility of the water column P pool beneath a shallow halocline.

Macroalgal-sediment nutrient interactions and their importance to macroalgal nutrition in a eutrophic estuary

Abstract: The potential for algal banks to influence water quality and sediment nutrient flux was examined through laboratory experiments and in situ monitoring of algal banks. Loose macroalgal banks displayed seasonal changes in tissue nutrient concentrations suggesting a strong dependence on water column nutrients. These banks fail to generate conditions suitable to sediment nutrient release. Dense banks generated low oxygen conditions in the inter-algal water (0–1 mg l−1), corresponding to zones of high, and relatively stable, phosphate and ammonium concentrations (up to 96 μg l−1 PO4P and 166 μg l−1 NH4N). Laboratory experiments confirmed that macroalgal banks can generate reducing conditions at the sediment surface, regardless of the aeration regime, through the decomposition of macroalgal tissue. Platinum electrode potentials as low as −200 mV were recorded in the inter-algal water. In such banks, redox-dependent sediment nutrient release and anaerobic accumulation of nitrogen accounted for inter-algal nutrient concentrations of over 60 μg l−1 phosphate and 800 μg l−1 ammonium. The generation of reducing conditions in inter-algal water required 7 days of still conditions and so this mechanism of nutrient generation is unlikely to be important in winter, when strong winds frequently shift the algal banks. It is suggested that in summer this mechanism may provide a source of nutrients to dense algal banks, supplementing reserves stored in winter.

A preliminary mass balance model of primary productivity and dissolved oxygen in the Mississippi River Plume/Inner Gulf Shelf Region

Abstract: A deterministic, mass balance model for phytoplankton, nutrients, and dissolved oxygen was applied to the Mississippi River Plume/Inner Gulf Shelf (MRP/IGS) region The model was calibrated to a comprehensive set of field data collected during July 1990 at over 200 sampling stations in the northern Gulf of Mexico The spatial domain of the model is represented by a three-dimensional, 21-segment water-column grid extending from the Mississippi River Delta west to the Louisiana-Texas border, and from the shoreline seaward to the 30–60 m bathymetric contours Diagnostic analyses and numerical experiments were conducted with the calibrated model to better understand the environmental processes controlling primary productivity and dissolved oxygen dynamics in the MRP/IGS region Underwater light attenuation appears relatively more important than nutrient limitation in controlling rates of primary productivity Chemical-biological processes appear relatively more important than advective-dispersive transport processes in controlling bottom-water dissolved oxygen dynamics Oxidation of carbonaceous material in the water column, phytoplankton respiration, and sediment oxygen demand all appear to contribute significantly to total oxygen depletion rates in bottom waters The estimated contribution of sediment oxygen demand to total oxygen-depletion rates in bottom waters ranges from 22% to 30% Primary productivity appears to be an important source of dissolved oxygen to bottom waters in the region of the Atchafalaya River discharge and further west along the Louisiana Inner Shelf Dissolved oxygen concentrations appear very sensitive to changes in underwater light attenuation due to strong coupling between dissolved oxygen and primary productivity in bottom waters The Louisiana Inner Shelf in the area of the Atchafalaya River discharge and further west to the Texas border appears to be characterized by significantly different light attenuation-depth-primary productivity relationships than the area immediately west of the Mississippi Delta Nutrient remineralization in the water column appears to contribute significantly to maintaining chlorophyll concentrations on the Louisiana Inner Shelf